The invention relates to a method for producing a 3D micro flow cell, consisting of a lower and an upper substrate between which is located a flow channel that is penetrated by an electrode structure connected to external contacts, wherein at least one of the substrates is equipped initially with a conductive trace and electrode structure and is provided at the ends of the flow channel with feedthroughs for connecting a fluid inlet and outlet. The invention further relates to a 3D micro flow cell produced using the method.
3D micro flow cells of this nature are used, for example, as cell manipulators for the handling and optical analysis of dielectric biological particles, in particular of cells and/or bacteria or viruses. To this end, the micro flow cells are equipped with a flow channel at the ends of which are provided one or more fluid inlets and outlets. Said fluid inlets and outlets are made by feedthroughs extending perpendicular to the flow channel, for example. The height of the fluid channel is generally in the range of a few micrometers, while the flow channel is delimited at the top and bottom by glass substrates and/or silicon substrates and at the sides by suitable channel walls. In order to be able to hold individual cells “freely suspended” at a predetermined location within the fluid channel, electrodes that generate an electrical field when a voltage is applied are located in the fluid channel. The electrostatically held cell can then be illuminated by suitable illumination and observed by means of a microscope.
A variety of technologies are generally known to make it possible to implement such three-dimensional structures. Thus, for example, a glass substrate can be wet chemical etched on one side in order to produce a flow channel therein and subsequently be joined by diffusion welding to a second glass substrate as the cover element. The requisite electrodes for handling cells or biological particles are previously applied to the first and/or second glass substrate by known photolithographic methods, and the second glass substrate is subsequently mounted face down on the bottom glass substrate.
However, the technology of diffusion welding is relatively expensive and the capabilities of generally isotropic glass structuring are limited. It can be considered a further disadvantage that only relatively coarse electrode structures can be applied to the structured glass surfaces. However, in order to be able to implement exact handling of individual cells or biological particles, an extremely precise geometric structure of the electrodes is necessary to be able to electrostatically manipulate these particles and hold them in place at the desired location in a noncontacting manner.
Another technology is described by Müller/Gradl/Howitz/Shirley/Schnelle/Fuhr in the journal “BIOSENSORS & ELECTRONICS,” No. 14 (1999), pp. 247–256. Described here is the application of the purely manual epoxy resin gluing technique, wherein first a polymer spacer is processed on a glass surface that has previously been equipped with platinum electrodes and electrically conductive traces. Then the glass substrate is coated outside the polymer structure with a synthetic resin, such as epoxy resin, as an adhesive and after that a second piece of glass, which likewise has been equipped with electrodes, is positioned thereupon and the bond is subsequently compressed. This assembly step is usually performed with a so-called die bonder (chip bonder).
There are difficulties here in that it is problematic to manufacture micro flow cells that always have exactly identical geometric dimensions and in which it is certain that no adhesive penetrates into the flow channel during the assembly process, something which would partially narrow the channel. The efficiency of this step is thus extremely poor and unsuitable for mass production.
Moreover, a so-called underfill technique has become known in which a first polymer (thick lacquer) is spun onto the glass substrate that is equipped with electrodes, wherein the thickness of the spun-on polymer is predetermined by the height of the channel provided. The positive channel system is then structured from this polymer, i.e. the excess thick lacquer is completely removed during this photostructuring. The second glass substrate is then aligned with and pressed onto the first glass substrate. The 3D arrangement obtained in this manner is held by lateral penetration of a creepable adhesive (underfiller), a second polymer, after which the channel system in the first polymer is washed out again with a solvent. The solvent must not attack the second polymer here. A particular disadvantage here is that no inner flow elements can be manufactured in the channel in this way because they cannot be reached by the second polymer. Moreover, this technique is extremely time-consuming and limited with respect to structural resolution.
The object of the invention is to disclose a method for producing a 3D micro flow cell that can be implemented economically and with which especially uniform geometric parameters can be achieved. The invention further has the object of creating a 3D micro flow cell that can be produced economically with the method according to the invention.